1. Field of the Invention
The present invention relates to storage cells and more particularly to a storage transistor.
2. Description of the Prior Art
In the applicant's earlier U.S. patent application Ser. No. 903,359 filed May 5, 1978, there has been proposed a semiconductor storage cell comprising a MI1I2S-field-effect transistor structure and a programming gate electrode in addition to a read gate electrode for permitting the non-volatile storing of an electric charge, and in which, between the two insulator partial layers I1 and I2, there is arranged a continuous storage medium extending throughout the entire widths of the read gate electrode and the programming gate electrode extending in parallel therewith. This semiconductor cell is to be regarded as a parallel arrangement of two field-effect storage transistors having a common source and gate region, as well as a common storage medium between the two insulating storage layers, but with two separate gate electrodes, and, therefore, is known as a tetrode storage cell.
Compared with a conventional MI1I2S-field-effect transistor, the tetrode storage cell according to the earlier proposal offers the possibility of a longer storage time by requiring a shorter programming time and, simultaneously, a lower programming voltage.